It is, therefore, highly probable that the paired ingrowths of the mesoblast from the lips of the blastopore may have been in the first instance derived from a pair of archenteric diverticula.
These cells soon divide, and at the same time pass out of the hypoblast, and enter the archenteric cavity (fig.
Its mode of origin may be compared with that in Amphioxus, in which an axial fold of the archenteric wall is constricted off as the notochord.
The Chordata, or at least the most primitive existing members of the group, are characterized by the fact that the body cavity arises as a pair of outgrowths of the archenteric cavity.
B and C, so, arise near the front end of the body and gradually extend backwards as wing-like diverticula of the archenteric cavity.
The section of the archenteric cavity in the trunk dilates and constitutes the permanent mesenteron (figs.
Paired archenteric outgrowths give rise to the whole mesoblast in Amphioxus (fig.
Paired archenteric pouches meanwhile appear at the sides of the axial notochordal tract, the mesoblastic somites.
Each outgrowth contains a prolongation of the archenteric cavity (compare figs.
That a notochord should develop out of the archenteric wall because a supporting axis would be beneficial to the animal may be a teleological assumption, but it is at the same time an evolutional heresy.
The formation of the permanent alimentary tract, when the hypoblast is so bulky that there is no true archenteric cavity, has been especially investigated by Bobretzky (No.
The segmentation and the invagination take place nearly as in Cassiopea, but the archenteric cavity is relatively much smaller, and the large space between it and the epiblast becomes filled with the gelatinous tissue which forms the umbrella.
A prominence on one side of the embryo now develops which forms the commencement of the foot, and the archenteric sack grows out at its free extremity into two lobes, but remains attached to the epiblast by an imperforate pedicle.
The blastopore becomes closed and the archenteric sack forms a small mass attached at one point to the walls of the embryonic vesicle (fig.
Owing to the elongation of the archenteric cavity the embryo assumes a bilateral form (fig.
Where it comes in contact with the wall of the body in front a small epiblastic invagination arises, which meets and opens into the archenteric sack and forms the permanent mouth.
In the case of epibolic invagination as well as in that of the type of delamination just spoken of, the archenteric cavity is in most cases secondarily formed in the solid mass of hypoblast (fig.
The blastopore gradually narrows, and finally closes, while at the same time the archentericcavity (fig.
In the first place a special mass of mesoblast cells appears at the hinder end of the archenteric sack; and becoming elongated transversely gives rise to the single adductor muscle.
The archenteric sack of Repiachoff is clearly the same structure as Barrois' four invaginated cells of the oral face, their further history has unfortunately not been followed out by Repiachoff.
The hypoblast cells in the succeeding stage arrange themselves round a central archenteric cavity, and at the same time rapidly increase in size and become filled with a secondary deposit of food-yolk.
The origin of the body cavity as paired archenteric diverticula has already been described.
From the nearly obliterated archenteric cavity outgrowths take place which give rise to the ciliated chambers.
It arises as a ciliated epiblastic ingrowth which meets the free end of the archenteric sack, fuses with it, and shortly afterwards opens into it (fig.
An invagination, presumably at the lower pole, now takes place, and gives rise to an archenteric sack.
The outermost layer of the protoplasm becomes, relatively to the inner layer, clear and transparent, and there thus arises an indication of a division of the walls of the archenteric cavity into two zones, or layers.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "archenteric" in a variety of sentences. We hope that you will now be able to make sentences using this word.
